Technology giant Apple says it cannot sell products online in Russia because the rouble's value is too volatile for it to set prices.

The company stopped sales of its iPhones, iPads and other products in the country after a day in which the currency went into free-fall.

The rouble has lost more than 20% this week, despite a dramatic decision to raise interest rates from 10.5% to 17%.

Early on Wednesday, the rouble was down 5% with one dollar buying 71 roubles.

Its all time low, set on Wednesday, saw one dollar buying as many as 79 roubles.

Apple last month increased its prices in Russia by 20% after the weakening rouble left products in the country cheaper than in the rest of Europe.

Russia's central bank said on Wednesday it had spent almost $2bn intervening in the currency market on Monday.

It has spent around $80bn trying to prop up its rouble this year, but despite that, the currency has lost more than half its value against the dollar since January, with cheaper oil and Western sanctions over its stance over Ukraine the chief factors.

Both of these have weakened the Russian economy.

Russia's central bank has pledged fresh further measures to try to stabilise its currency, with First Deputy Governor Sergei Shvetsov describing the situation as "critical".

The rouble's slide this week was prompted by fears that the US was considering a fresh set of sanctions against the country for its support for separatists in Ukraine.